1. Field of the Invention
The present invention relates to a quantitative asymmetry method and, particularly, to a method of quantifying asymmetry of an object. A symmetry value is developed from the quantified symmetry method. Based on the discovered Optimal Symmetry Plane (OSP), slanted images from medical imaging can be rectified.
2. Description of Related Art
Due to advancement in the medical field, medical images have become an important tool for pre-surgical planning for oral, maxillofacial, and plastic surgery. Medical imaging may be two-dimensional (2-D) or three-dimensional (3-D) images, and the images assist physicians in obtaining a full picture of the nidus of each individual patient. In addition, a symmetric face of an individual is much more attractive esthetically than an asymmetric face. However, a completely symmetric face is virtually impossible in nature.
In general, medical images are obtained by x-ray, ultrasound, Computer Tomography (CT) or Magnetic Resonance Imaging (MRI), and the obtained medical images are 2-D images. Furthermore, multiple 2-D images are used to construct a 3-D image, and using more 2-D images increase visual spatial realism of the 3-D image. A traditional method of constructing a symmetry plane of a 3-D image model for a surgeon is to manually draw an approximated central plane on the 3-D image model. The 3-D image is presumed to have a symmetry plane based on the central lines of the skull, and, further, the lateral half of the 3-D image is mirrored accordingly. That means the lateral half of the 3-D image is constructed based on the presumed symmetry plane generated from the processed 2-D images.
In general, the central symmetry line of one 3-D image model is determined subjectively by an individual surgeon. However, each patient is unique, and various parts of the body are asymmetric to varying extents. Further, each surgeon has a slightly different but distinct esthetic sense. Furthermore, a single surgeon may draw different central lines on the same medical image in different circumstances. Therefore, how to determine a unique, reasonable and reliable symmetry plane of a 3-D image model is crucial for plastic and maxillofacial surgery.
A few publications relate to determining symmetry of an object and are particularly applicable to digital images. Josef Bigun proposed a method to find the best symmetry region in certain patterns. Bigun's proposed method uses a symmetry equation and derives the best symmetry region by transforming the symmetry equation into a specific spectrum with a least square method. In another publication, Hagit Zabrodsky, Shmuel Peleg and David Avnir proposed an edge verification method to quantify the symmetry level of the object.
These methods described above are able to determine the symmetry of a specific object but require extensive and complex computations in data processing. Even though promoting computational performance during the determination of the symmetry of an object and developing a novel method to evaluate the degree of symmetry of an object are stated objectives in the field, actually obtaining a reliable and consistent degree of asymmetry is the key issue.
The present invention provides a way of quantitatively determining symmetry of an object to overcome the aforementioned problems.